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Intro to Controller Area Networks (CAN) Part 1 of 2, E. Zivi, April 1, 2015 References: 1.A CAN Physical Layer Discussion Microchip Application Note AN00228a 2.Controller Area Network (CAN) Implementation Guide Analog Devices Application Note AN-1123 3.Controller Area Network, CANPRES Version 2.0, Siemens Microelectronics, Inc., October, 1998 4.http://www.kvaser.com/en/about-can/the-can-protocol.htmlhttp://www.kvaser.com/en/about-can/the-can-protocol.html 5.http://www.kvaser.com/can-protocol-tutorial/http://www.kvaser.com/can-protocol-tutorial/ 6.CAN physical layer ref: http://www.can-cia.org/index.php?id=systemdesign-can-physicallayerhttp://www.can-cia.org/index.php?id=systemdesign-can-physicallayer 7.Controller Area Network Physical Layer Requirements, TI SLLA270January 2008 8.CAN Tutorial, http://www.computer-solutions.co.uk/download/Peak/CAN-Tutorial.pdfhttp://www.computer-solutions.co.uk/download/Peak/CAN-Tutorial.pdf 9.CANopen Introduction, ref: http://www.canopensolutions.com/english/about_canopen/about_canopen.shtmlhttp://www.canopensolutions.com/english/about_canopen/about_canopen.shtml 9.Embedded Networking with CAN and CANopen, by Pfeiffer, Ayre and Keydel 10.CAN open Implementation: Applications to Industrial Networks, by Farsi and Barbosa 11.CS4700/CS5700 Fundamentals of Computer Networks, Alan Mislove, Northeastern University 12.Controller Area Networks http://electrosofts.com/can/index.htmlhttp://electrosofts.com/can/index.html

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CAN History 1.In 1985 Bosch originally developed CAN, a high-integrity serial bus system for networking intelligent devices, to replace automotive point-to-point wiring systems. 2.As vehicle electronics became pervasive, complex wire harnesses which were heavy, expensive and bulky were replaced with CAN throughout the automotive industry. 3.In 1993 CAN became the international standard known as ISO 11898. 4.Since 1994, several widely used higher-level protocols have been standardized on top of CAN, such as CANopen* and DeviceNet. 5.In 1996 the OnBoard Diagnostics OBD-II standard which incorporates CAN becomes mandatory for all cars and light trucks sold in the United States. 6.Today markets including surface transportation, industrial automation, maritime and avionics systems have widely adopted CAN. 7.Today CAN is incorporated into many microcontrollers (our mbed has two CAN ports ) * Well investigate this higher level protocol once we cover the CAN basics 2

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Vehicles Before CAN: Expensive, bulky point to point wiring, wiring harnesses and many connectors. Vehicles After CAN: Systems of Systems with multiple CAN busses, simplified wiring harnesses and many Fewer connectors Before CAN After CAN

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CAN is Now Central to Automotive Networks New cars typically contain 50 to 100 microcontrollers

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Advantages of CAN 1.Low cost network infrastructure which is often built into microcontrollers. 2.Large market segment with broad availability of hardware, software and systems engineering tools. 3.Light weight, low latency, highly deterministic design specifically for real-time embedded applications. 4.Reliable with strong error detection, fault tolerant versions available. 5.Flexible and highly configurable with various higher level application protocols. 6.Foundation for next generation technology controller area networks. 5

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CAN & International Standards Organization (ISO) Open Systems Interconnect (OSI) Reference Model 6 High level CAN Protocols implement Application layer and skip the four intervening layers

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In Future Classes Well Introduce The CANopen Application 7 High level CAN Protocols implement Application layers and skip the four intervening layers ISO 11898 CAN Data Link Layer ISO 11898 CAN Physical Layer Application CiA 301 CANopen Application Layer & Communication Profile CiA 302 CANopen Framework for CANopen Managers & Programmable Devices CiA 4xx Device Profiles CiA 401 Generic I/O Profile CiA 402 Motion Control Profile IEC 61131-3 Programmable Devices Profile Not Implemented by CAN or CANopen

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CAN Data-Flow Model One node transmits, all nodes listen and processor data frames selectively. Message filtering is typically performed in transceiver hardware. This data flow supports a broad range of network communication models: 1.Master / Slave : All communications initialed by master node 2.Peer-to-Peer : Nodes interact with autonomously with equal authority 3.Producer / Consumer : Producer nodes broadcast (push) messages to Consumer nodes 4.Client / Server : Client nodes request (pull) data from Server nodes CAN NODE 1 Receives Message CAN NODE 2 Transmits Message CAN NODE 3 Ignores Message CAN NODE 4 Receives Message 8

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CAN Bus Broadcast Animation Mouse over graphic to control animated CAN message example

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CAN Typical High-Speed Physical Layer CAN uses differential signaling to improve signal to noise ratio. Termination resistors reduce signal reflection. Idle bus state is Recessive with no applied differential signal: V CAN_H V CAN_L Dominant state occurs when one or more nodes drive the bus state to: V DIFF 10

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CAN Differential Bus Interface Transceivers The CAN idle state presents a recessive state, signaled by a small differential voltage across CANH and CANL. With the indicated split termination, this idle voltage will be halfway between VDD (positive supply) and VSS (ground). The CAN dominant state occurs when one or more transceivers simultaneously close the indicated transistor switches driving CANH and CANL toward VDD and VSS, respectively. This open collector transistor switch configuration is referred to as a wired or since any node transmitting a dominant bit always overrides a recessive bit. Since a dominant bit represents a logic 0, this arrangement is sometimes referred to as wired and since bus a logic 1 state is achieved only if all nodes (node 1 AND node 2 AND node 3 ) signal logic 1 recessive bits). Micro- controller Transceiver Additional Transceivers Transistor Switches 60 Split Termination Example Capacitive coupling to ground 11

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Example of a Wired OR Closing Node A switch OR closing Node B switch turns on the light. Conversely, the light is off unless Node A switch is open AND Node B switch is also open. 12

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Example CAN Sample Signaling 13 Dominant bus state = logic 0 Recessive bus state = logic 1

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CAN Logic & Arbitration 1.CAN 2.0A messages begin with an 11-bit message ID which identifies the message type and also establishes the message priority. 2.As with many computer interfaces, the CAN transceivers invert the microcontroller signal. Thus, the dominant bus state occurs when a logic 0 is transmitted and the recessive state occurs when a logic 1 is transmitted. 3.CAN uses the message ID to perform bus access arbitration between nodes. 4.Each node waits for an idle bus state then begins to transmit its message ID. 5.Each node also listens to the bus to see if the bus state match its transmission. 6.If a node detects a dominant bus state while transmitting a recessive message ID bit (logic 1), it drops out of the current arbitration round and will try again the next time the bus is idle Coming up: CANarbitration.gif animated bus arbitration example 14

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7-bit CANopen Node ID Arbitration Example

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CAN Arbitration Animation Mouse over graphic to control animated bus arbitration example 16

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Key Advantages of CAN Bus Arbitration 1.Fast & deterministic. 2.Highest priority message gets immediate access once the bus is available. 3.Arbitration is essential free since message ID encodes message priority. 4.Unlike Carrier Sense Multiple Access with Collision Detect (CSMA/CD) arbitration propagation delays never cause message collisions.

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CAN Data Frame Format 18